Vacuum pump



Dec. 28, 1943. J. DUBROVIN 2,337,849

VACUUM PUMP Filed March 14, 1939 2 Sheets-Sheet 1 63 72 Z I h: 70 71 71 x INVENTQR. J7 J5 13 John flab/00678,

Qlmzh ///m% ATTORNEYS Dec. 28, 1943. J. DUBROVIN 2,337,849

VACUUM PUMP Filed March 14, 1939 2 Sheets-Sheet 2 Joiznflabmuai,

ATTORNEYS Patented Dec. 28,1943

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VACUUM PUMP John Dubrovin, Chicago, 111.,assignor to W'. M. Welch Manufacturing Company, Chicago, 111.,

a corporation of Illinois Application March 14, 1939, Serial No. 261,803 12 Claims. (Cl. 230-205) This invention has to do with rotary oil sealed vacuum pumps, such as are used in the production of extremely highvacuums, and isparticularly concerned with pumps of the type wherein the rotor is provided with two or more outwardly spring-pressed vanes for sliding engagement with the surrounding wall of the stator and wherein the rotor is eccentricaily mounted in the stator and turns in an arcuate seat in the latter which has the same radius of curvature as the rotor.

.The purpose of the invention is to provide an improved pump of the type described which is capable of producing a higher vacuum than has heretofore been possible with other pumps of the same general type.

The improved pump is characterized, among other features, by a novel construction and arrangement of the exhaust port in the finishing stage, which insures rapid and complete evacuation of all the oil in front of the vanes as the latter approach the seat; the provision of a chamber between the finishing and roughing stages, which receives oil from the finishing stage and feeds it back to that stage for recurrent circulation; and a novel construction and arrangement of the seat in the roughing stage, which allows free fiow of all excess oil baclr to the pumping chamber, reduces the flow of oil across the seat tothe intake side of the latter, and allows the volatiles pushed into the seat to free themselves from the oil before the latter reaches the intake side. This last mentioned feature is applicable to single as well as two-stage pumps.

While the foregoing statements are indicative in a general way of the nature of the invention,

other more specific objects and advantages will,

be apparent to those skilled in the art upon a full understanding of the novel features which form the subject matter of the invention.

A preferred embodiment of the invention'is presented herein for the purpose of exemplification, but it will of course be appreciated that the invention is susceptible of incorporation in other structurally modified forms coming equally within the scope of the appended claims.

In the accompanying drawings:

Fig. .1 is a side view of a two-stage vacuum 7 pump constructed in accordance with the invention;

Fig. 2 is a view of one end of the pump, with' the main oil reservoir and the exhaust port for the roughing stage shown in section;

Fig. 3 is a view of the other end of the pump, with the housing about the inlet port for the finishing stage shown in section;

Fig. 4 is a vertical longitudinal sectionthrough the pump, taken on'the line'4-4 of Fig. 2;

Figs. 5, 6, 7, 8, 9 and 10 are vertical transverse sections through the pump, taken respectively on the lines 5-5, 6+6, 1-1, 8, 99 and Ill-l0 ofFi .4; I v h Fig. 11 is a fragmentary radial section through one end oi the pump, taken on the line Il-Ii of Fig. 2;

Fig. 12, is a fragmentary section, taken on the line l2-l2 of Fig. 6, showing the arcuate seat forthe rotor in the finishing stage; and

Fig. 13 is a fragmentary section,,taken on the line l3-I3 of Fig. 9, showing the arcuate seat for the rotor in the roughing stage.

The two-stage pump shown in the drawings includes a casing l0 which is composed of an end plate II, a stator ring, a center plate It, a second stator ring it and a second end'plate I 5. These parts are all tightly clamped together, in the order named, by a plurality of bolts l6, which bolts are screwed from opposite sides of the casing into the center plate IS. The stator ring l2, with the end plate I land center'plate l3, forms the pumping chamber ll of the finish-- izm stage of the pump. while the stator ring H, with the center plate I 3 and end plate l5,,forms the pumping chamber [8 0i the-roughing stage of the pump. The pump is adapted to be operated by an electric motor .(not shown), through a shaft l9 which is journaledin bearing apertures 20, 2| and 22 formed respectively in the end plate ll, center plate l3 and end plate IS. The pumping chambers l1 and I8 are circular in' shape,

and the shaft l9 passes through both chambers at points a little above their centers.

The chamber ll of the finishing stage contains a circular rotor 23 which is somewhatsmaller in diameter than the chamber and is located in the upper portion of the latter. The shaft l9 passes through an aperture 24 in the center of the rotor 23 and is secured to the latterby one or more keys 25. The rotor 23 is provided with diametrically opposed radial slots 26 in which two outwardly spring-pressed vanes 21 are slidably mounted with their outer ends in sliding engagement at all times with the peripheral wall of the chamber IT. The upper part of the rotor 23 slidingly contacts with the wall of the chamber I! at the top of the latter, in a closely fitting arcuate seat 28 which has the same radius of curvature as the rotor and is in continuous contact therewith throughout the angle indicated by the arrow 29. The rotor 23 and the vanes 21 are of the same width as the chamber I! and slidinsr y iengage at theirv sides with the opposed tacesoi 'the'end plate II and center plate II.

28 aroundthe rotor 23' tc'the other side of the seat.- r r IAn inlet port "so islocated at that side of the seat 28 ironiiwhich thevanes 2'! leave the seat, 7

and an :exhaust port]! islocated'at that side of .theseatat which the vanes enter the seat.

The inlet port '30 is formed in the peripheral,

wall of the'chamber i 1, while the exhaust port 3| is 'formed in the iaceo'fthe ccnterplate H at oneside of the chamber. The exhaustport 3I leads d'rom thelchamber l1 into a small center chamber "32 which is located inside of the center platefllat a point above the bearing aperture 2i for the shaft IS. The exhaust port also communicateswithin thepumping chamber IT, with asha'llow arcuate groove? in the face of the center plate I'J, which'groove'extends to a point at one side ofth'e front or high pressure edge of the seat 28 and *there connects with a. down wardly;extendinggroove '84 in the face of the center piate 18, which latter groove in turnoconnectsJat its loweren'd'with'a circular cavity l which surrounds the shaft IS. The cavity 35 opens into the center chamber 32 and, incidentally is' made suflicientlydeepto accommodate-'a'collar 36 'which ispinned to the shaft Iii to prevent endw se-movementfof thelatterQ An arcuate-grocve' 31,, similar in both size and shape vto the groove 33 is located in theface' of the end plate iL'directly-opposite the groove 33, and

connects, like thevgroove'. with'a downwardly extending groove '38 which terminates at its lowerien'd in a circular cavity 39 formed inJthe faceo-f the-endplateil about the shaft iii. A

narrow icross'groove :40 is provided in, the

peripheralwall of the chamber". atfthe front which is setat a slight angle inorder. to prevent the outer' edges'oi' the vanes .21 from catching a ainst the I same} extends across the chamber from oneside tothe other andconriects at its, ends' with the arcuate grooves" and 31. at 1 points substantially in line with the downwardly ext nding grooves-"34 and 38. The vessel'or otherpieceof equipment which is to be exhausted is connected by a suitable conduit (not shown) toanipple II which is screwed into the "top of a: small rectangular'housing Q2 mount d ontop' ofth'ezstator ring; The hous- .ing .MQWhIch-is cIamped ti htly in place by bolts 43 which screw intostudsl carried by the ring, provides aasealed enclosure for a passage H 48for the shaft 19; is secured'to the shaft'by througha wideangleil, and is provided with like the pumping space within the chamber I1- is crescent-shaped, and extends from one side of the seat 50 around the rotor 41 to the other side of the seat. An inlet port 53 is located near the low pressure edge of the seat Ill-which is theend of the seat from which the vanes leave tends upwardly through the peripheral wall of the chamber I 8; at a point immediately in advanc o'f the edgeof the seat 50, and is characterized by two relatively small branch openings '55 which are arranged side by side in the .wall. 7 r v A narrow cross groove 56 is formed in the arcuately extended seat 58 about midway be- 1 tween the high and low pressure edges of the seat. This groove, which is set at a slight angle, extends entirely across the seat from one side of the chamber to the other and connects at its ends with the upper .ends of two downwardly inclined grooves 51 and 58, which latter grooves are formed opposite each other in the faces of the center plate I3 and end plate l5. The'grooves ,51 and 58 pass to one sid of the bearingapertures 2i and 22 in the plates and terminate at points-59 and til-within the effecedge or the sealing seat 28. 'I'his, roove 40,

thereof. The opening 13 is normally closed by .-keys l9,' contacts'with an arcuate seat 50 in the 7 topof the'peripheral wall 01' the chamber I8 outwardly spring-pressed vanes 82 which slid-' V ingly;v engage .at': their outeri-ends"with the peripheralwwallot the chamber and along their sideedges withthe side walls of the chamber.

Thepumping'space within the chamber I8- .tive pumping space of the chamber l8, which points are more than removed from'the inlet port53 measured in the direction of rotation of the rotor 41, whereby one or the other of the vanes 52 will always provide a sealed partition in the chamberrl8 between the inlet port 53 and thelower ends of the grooves 51 and 58 regardless of the position of the rotor.

The outlet port 54 extends upwardly from the top of the stator ring ll into a vertically extending tube 6| formed in a fitting 62 which is located withinan oil reservoir 63. The'fitting 62 is secured to the top of the ring by screws 64, andthe reservoir 631s secured ,to the top of the ring about theQfitting-by bolts 65. A downwardly springpres'sed flap. valve 66, in'the form of a thin-leaf spring; is positionedover the top of the outlet tube 6|, and is helddown at one end by a screw stud 81; Whichstud also serves to support an open-workbafi'le 68 in a; position'about the top of the fitting; v r f The top of thefitting 62 and the flap valve 66 at the upper end of the outlet tube 6| are adapted to..be submerged in a body of oil contained with- 'in the reservoir 63. The reservoir is adapted the oil being indicated respectively by the marks v I0 and II provided on glassed-in observation windows 12 mounted in the end walls of the reservoir. The reservoir-is adapted to be filled with the oil through an opening 13 in the top a vented screw cap 14. The air or other gas exhausted from the vessel being operated on is forced upwardly through the outlet tube 6!, raises th flap valve 66, bubbles up through the body of oilin the reservoir, and passes off into the atmosphere through the vents in the cap 14. f

The oil in the reservoir, in entering the pump to lubricate the same, passes downwardly through atube l5 inothe fitting 62. The tube 15 has its slot in the rotor.

clined duct 11 in the end plate l5. The duct 3 11 connects at its lower end with an annular channel 18 provided in the bearing aperture 22 in the end plate I5. This channel "is inter.- sected by a groove 18 which extends from the channel to the inner face of the end plate. The oil used in lubricating both stages of the pump flows along the shaft l9 through the groove I8 to the near face of the rotor 41. Escape of oil in the opposite direction along theshaft is prevented by an oil sealing unit 88 of any suitable construction which fits about the shaft on the it will both seal and lubricate the contacting surfaces of all of the relatively movable working parts. After the pump has been runbutashort time some of the oil will accumulate in the bottom of the center chamber 82, between the finishing and roughing stages," and will re-circulate outside of the end plate i5 and is secured to the plate by screws 8|.

From the face of the rotor 47 the oil enters the roughing stage of the pump through two diametrically opposed grooves 82 in the rotor 41,

which grooves momentarily register with the groove IS in the end plate l5 during every revolutionof the rotor. The grooves 82 extend from one face of the rotor to the other along the shaft and intermediate their ends intersect with radially disposed holes 83 in the rotor and shaft, which holes contain the spring means 84 employed for pressing the vanes 52 outwardly in the The holes 83 open into the bottoms of the slots and the oil upon entering these slots from the holes 8 3 lubricates the vanes 52, the faces of'the rotor 41, and all other surfaces within the chamber l8 of the roughing stage. 7

The oil for the finishing stage of the pump travels from the groove!!! in the end plate througha third groove 85 in the rotor 41, which latter groove, like the grooves 82 in the rotor,

registers with the groove 19 during every revolution of the rotor. The groove 85 continues without interruption to the far face of the rotor 41 and there feeds its oil directly to the bearing aperture 2| in the center plate i3. This all travels along the shaft IS, in a thin film between the shaft and 'the bearing aperture, enters the cavity 35 in the far face of the center plate I8,

from there back into the finishing stage, the only additional oil entering the finishing stage from then on being raw oil which passes directly into the same from the reservoir 63 through the enclosed duct provided by the special groove 85 in the rotor 41, without first passing through the pumping chamber of the roughing stage. I

In this pump a substantial improvement resides in the provision of means for effecting quick removal of all the oil with its gaseous volatiles at the exhaust port of the finishing stage, which means acts to reduce the amount of gaseous molecules carried into and through the rotor seat in the stage. Instead of the usual circular ex-. haust port heretofore employed in pumps of this type the additional groove 48 is incorporated,

"which groove extends the full width of the stator ring I: so that morecomplete exhaustion of-all oil in front of the vanes is ffected and not merely that portion passing directly across the path of the-exhaust port, thus reducing the amount of foil and volatiles compressed into and through and finds its way from there to all of the work ing surfaces of the rotor 28 and vanes 21. The

far end of the shaft l9 and thebearing aperture 20 surrounding the same in the end plate II are sealed off from the atmosphere by a small plate- 86 which is secured to the outer faced the end plate II by screws 81. a v

The oil contained in the reservoir 88 may be drained from the same by removing a knurled screw plug 88 which is located Just below the bottom of the reservoir in a threaded duct 88 which communicates with a small sump 98 in the upper portion of the stator ring I. The oil which has accumulated in the center'chamber 32 in the center plate 13 may be drained from that chamber by removing a, small plate 8! at one end of the same, which plate is held in place by screws 92.

Befor starting the pump the reservoir 53 is filled with a good quality of oil, to approximately the level 69. As soon as the pump is started a certain amount of this oil will immediately find its way into all the cavities of the pump, where the seat. 7 v This high vacuum or finishing stage of the pump, it will be noted, is in direct series with the low vacuum or roughing stage of .the pump,-

and all oil which is discharged from the exhaust port of the finishing stage flows freely under the reduced pressures of the roughing stage to the center cavity 32. The gaseous content of the gaseous space above the oil in this center cavity is at a lowerpressure than that of the atmosphere by virtue of the pumping effect of the roughing stage. V I

In any mechanical device of this general'type there is the possibility of the higher. pressures achieved in the roughing stage finding some channel 'of entry by which they may increase the internal pressures of the finishing stage and thereby impair the efficiency of the finishing stage. The center cavity 82 insures'against any. such impairment in the present pump by providing'in effect an oil seal between the finishing stage-and the roughing stage so that any gaseous content within the roughing stage which by virtue pr its higher pressure might find access to the finishing stage will first be liberated in this center cavity. Thus this same gaseous content is exposed to the intake of the roughing-stage, and instead of such leak forming a direct path into the finishing stage this reservoirof oil in the centercavity will provide a direct path for such gaseous pressure to return directly to the roughing stage without interference with the performance of the finishing stage. i 7

Another noteworthy feature of the improved pump is the effect of the groove 58 and connecting' grooves 51 and 58 in dividing both the seat and the pumping chamber of the roughing stage into twoareas of oil circulation, the area in advance of the seat being what might be termed a w wet area and the area beyond the seat being a dry area. This groove 56 midway of the seat;

by communicating with the side grooves 51 and 58, provides a free path for the flow of oil and volatiles therefrom along the sides of the rotor Y to a. point in'the roughing stage chamber removed a little more than from the intake port 53. Such point in the stator cavity is far extreme compression will nothave been achieved within the pumping chamber at that point. Thus it will beseen that the groove llserves two purposes-it allows a ireeiiow of all of the excess amount or oil back to ,the-stator cavity of the asemee roughing stage at a point removed 180 irom'the intake port, and it also allows those volatiles whichare pushed into :the seat 50 by the preceding ,vane 52 to free themselves iromthe oil in'the seat, by again taking on theirgaseou's form, to return quickly to thestatorcavity at the point described. Being led into the stator cavity at: a point removed 180 from the seat, this excess of oil and the volatiles which free, themselves i'rom the oil within the seat are placed directly ahead of the next vane and again forced against the exhaust port 55, under the compression of that vane.,,,

'Ihe'result of this construction is that twoareas are providedwithin the roughing-stage or the pump, which mightbe'described as a wetlside, and a dry side. The wetlsideeincludes th last portion oi the stator cavity, whichis re oved 180 from the intake port 53, and the first half oi. the seat 50. To this area. all excess of oil within the roughing stage is confined and the liquid-for gaseousdenslty from volatiles liberfated or compressed within the oil at low pressures is kept high, This is in contrast to the irelatively dry side ofthe roughing stage, which is located 1 at the intake side'and includes allthe area of the stator cavity up to a point 180 fromthe inshort of the, center of the seat takeand in the other direction up to a point just 50. In this area shaped pumping chamber present between the stator and rotor, inlet and outlet ports in the pumping chambe'rat oppositesides of the arcuateseat, and a cross groove in the surrounding cylin.

, drical wall or the stator at the edge of the high pressure side or the seatincommunication with the outlet port, which groove is set at an angle to the outer edges of the vanes crossing the same.

2. In a rotary oil sealed vacuum pump for producing extremely high vacuums, the combination with a roughing stage, of a finishing stage alongside the roughing stage having a hollow generally cylindrical stator, a circular rotor which is eccentrically positioned in the stator and is provided with two or more outwardly spring-pressed vanes for sliding engagement with the surrounding cylindrical wall'of the stator, an arcuate. seat in said wail of the sameradius of curvature as the rotor," in which seat the rotor turns, means for supplying oil to the crescent-shaped chamber present between the stator and rotor, an inlet port in the surrounding cylindrical wall of the it is desirable" to have extreme freedom from an I excess or oil and extreme i'reedom from they gaseous volatiles which to whatever extent they are present impede the fiow of gaseous molecules being pumped away from the finishing-stage.-

The groove 58 in the stator ring and the connecting path from said groove to the points 59 and 60 in the stator cavity produce this condition and represent a fundamental advance in pumps of this general type. "It will be appreciated that the improvements embraced within this invention relate to the definite control or the areas within the pump to which the high gaseous content and excess of oil are confined. By keeping the areas of excess oil and highgaseous content within a cycle which recurrentlyleads'jback to the exhaust port and never reaches-a Iree'path to theintake port eillciency and effectiveness have been greatly augmented; Q

The device or the preceding paragraph eil'ectively increases the ability of the pump to discharge gas molecules and thereby lower the order 01' the pressure" which is the eifective limit the:

pump can achieve. Pumps ofvery similar design without thisieature of single cavity showed a practical limit or not less than .02 mm. of mer-, cury pressure while pumps including this feature,

(single cavity) attain a limit .001 mm. and with two cavities as described herein .00005 mm. i

I claim:

ducing extremely high vacuums, a hollow gen- 1. In a rotary oil sealed vacuum pump for proerally cylindrical stator, a circular rotor which,

is eccentrically positioned in the stator and is provided with two or more outwardly springpressed vanes'for sliding engagement with the surrounding cylindrical wall of the stator, an

arcuate seat in said wall of the same radius of curvature as the rotor, inwhich seat the rotor turns, means for supplying oil to the crescent-V stator at one side of the arcuate seat, an outlet port in ,one oi the side walls of the stator at the opposite sideot the seat in communication with the roughing stage, and a cross groove in the surrounding cylindrical wall'of ,the stator at the edge of the high pressureside of the seat in communication with the 'outlet port,'which groove is set at an angle to the outer edges of the vanes crossingthesame. d V

3. In a rotary oil sealed vacuum pump for producing extremely high vacuums, roughing and finishing stages havingc'rescent shaped pumping chambers arranged alongside eachother, an exteriorly accessible oil reservoir vented to the atmosphere, means for supplying oil from the reservoir to each stage of the pump without requir ing the oil for the finishing stage to first pass through the pumping chamber of the roughing stage, an inlet port for the finishing stage, an

outletport for the roughing stage opening into chamber, and means isolated fromdirect communication with the inlet port of the finishing stage for conducting oil from the center chamber 'back to the finishing stage.

4. In a rotary oil sealed vacuum pump for producingzextremelyhigh vacuums, a casing containing roughing and finishing stages, said casing beingcomposed of a center plate, two stator rings at opposite sides of the center plate, and two end plates at the far sides of the stator rings, one of the stator rings with the center plate and'one of the end plates forming the I pumping chamber of the roughing stage of the pump, and the other stator ring with the center plate and the other end plate forming the pumping chamber of the finishing stage, an oil reservoir. mounted on the stator ring of the roughing stage,a drive shaft journaled in bearing apertures, in the center plate and end plates eccentrically' of the stator rings, rotors on the shaft in the pumping chambers'of both stages turning in arcuate seats i'ormed in the peripheral walls of the stator rings, said rotors being provided .with outwardly movable vanes for sliding engagement with said peripheral walls and the arcuate seats therein connecting ducts in the stator ring of the roughing stage below the reservoir, in the adjacent one of said .end plates and in the rotor in the roughing stage for supplying oil from the reservoir to each stage with the oil for the finishing stage passing through a separate enclosed duct in the rotor in the roughin stage, an inlet port for the finishing stage, an outlet port for the roughing stage discharging into the oil reservoir below the oil level therein, a center chamber in the center plate above the bearing aperture therein for receiving oil from the finishing stage and returning it to the same, an outlet port for the finishing stage opening into the center chamber, an inlet port for the roughing stage opening into the roughing stage from the center chamber, and means for conducting oil from the center chamber back to the finishing stage.

5. In a rotary oil sealed vacuum pump for producing extremely high vacuums, a hollow stator, a circular rotor which is eccentrically positioned in the stator and is provided with two or. more outwardly spring-pressed.vanes for sliding engagement with the surrounding wall of the stator, an arcuate seat in said wall of the same radius of curvature as the rotor in closely fitted association therewith throughout a substantial arc whereby to produce an arcuate seal between the stator and rotor and allow only the passage of a thin film of lubricating oil from one side of the seat to the other, said stator forming with the rotor a crescent-shaped pumping chamber which extends frorn one side of the seat about the rotorlto the other side of the seat, a low pressure inlet port in the chamber at one side of the seat, a high pressure outlet port in the chamber at the other side of the seat, means for supplying oil to the 'chamber, and a by-pass between a portion oi. the seat and the chamber at a point in the latter which is more than 180 from the inlet port and is sealed oil from the inlet port at all times by at least one of the vanes, which by-pass permits any volatiles from the oil within the seat to return directly to the high pressure side otthe chamber and permits any excess oil oil within the seat to also return to the high pressure side, whereby to leave the portion of the seat beyond the by-pass and the low pressure side of the chamber relatively free of volatiles and excess oil.

6. In a rotary oil sealed vacuum pump for producing extremely high vacuums, a hollow stator, a circular rotor which is eccentrically positioned in the stator and is provided with two outwardly spring-pressed vanes for sliding engagement with the surrounding wall of the stator, an arcuate seat in said wall 01 the same radius of curvature as the rotor in closely fitted association therewith throughout a substantial arc whereby to produce an arcuate seal between the stator and rotor and allow only the passage of a thin film of lubricating oil from one side of the seat to the other, said stator forming with the rotor a. crescent-shaped pumping chamber which extends from one side 0! the seat about the rotor to the other side of the seat, a low pressure inlet port in the chamber at one side of the seat, a high pressure outlet port in the chamber at the other side of the seat, means for supplying oil oi the seat and the chamber at a point in the latter which is more than 180 from the inlet port and is'sealed oil? from the inlet port at all times blfit leastone of the vanes, which by-pass communicates also with, the side' faces of the rotor at oppositely disposed points adjacent the seat, said by-pass permitting any'volatilesfrom the oil within the seat'to return directly to the high pressure side of the chamber and permitting any excess of oil within the seat to also return to the high pressure side, whereby to leave the portion of the seat beyond the by-pass and the low pressure side of the chamber relatively free oi volatiles and excess oil.

7. In a rotary oil sealed vacuum pump for producing extremely high'vacuums, a .hollow generally cylindrical stator, a circular rotor which is eccentrically positioned in the stator and is provided with two or more outwardly springpressed vanes for sliding engagement with too surrounding cylindrical wall of the stator, an arcuate seat in said wall of the same radius of curvature as the rotor, in which seat the rotor turns, means for supplying oil. to the crescentshaped pumping chamber present between the stator and rotor an inlet port in the pumping chamber at the low pressure side of the seat, a circumferentially extending groove in one of the side walls of the pumping chamber at the high pressure side-of the seat, which groove extends back away from the seat along the path of approach of the vanes, a cross groove in the cylindrical peripheral wall of the stator at the edge of the high pressure side of the seat in communication with that end of the circumferentially extending groove which is nearer the -seat,'and an outlet port in communication with the circumferentially extending groove.- l

8. In a rotary oil sealed vacuum pump for producing extremely highvacuums, a hollow generally cylindrical stator, a, circular rotor'which is eccentrically positioned in the stator and is provided with two or more outwardly springpressed vanes for sliding engagement with the surrounding cylindrical wall of the stator, an arcuate seat insaid wall of the same radius of curvature as the rotor, in which seatthe rotor turns, means for supplying oil to the crescentshaped pumping chamber present between the stator and rotor, inwardly extending grooves in the opposed side walls of the pumping chamber at the high pressure side of the seat, a cross groove in the cylindrical peripheral wall of the stator at the edge of the high pressure side of the seat in communication at its ends with the outer ends of the inwardly extending grooves, and an' outlet port in communication with the cross groove, said cross groove and inwardly extending grooves being disposed in the paths of travel respectively of the outer edge and side edges of each or the vanes.

9. In a rotary oil sealed vacuum pump for pro-' to the chamber, and a by-pass between a portion 7 circumterentially extending grooves in the 0p- 6 7 aaaasso posed side walls orthe pumping chamber at the high pressure side of the seat, which grooves extend back'away from the seat along the'path or approach of the vanes,- inwardly extending grooves in the opposed side w'allsorthe pumping chamber with their outer ends in communication with the ends of the circumferentially extending grooves which arenearer the'seat; a cross groove in the cylindrical peripheral wall. of the stator at the edge of the high pressure side of the seat in communication at its ends-with the connecting ends of the circumferentially extending grooves andrinwardly extending grooves, and an outlet port in communication with one otthe ,circumferentially extendinggrooves, said cross groove and inwardly extending grooves being disposed in the paths of travel respectively or the outer" edge and side edges of each of the vanes. v

10." In a rotary. oil sealed vacuum'pump for producing extremelrhigh' vacuums, ahollow circumrerentially extending grooves, said cross groove being set at an angle'to the outer edges of the vanes crossing the samejand said inwardly extending grooves being set at an angle to the 'side'edges of the vanes, said cross groove and inwardly extending grooves being disposed in the paths of travel respectively of the outer edge and side edges of each of the vanes.

generally cylindrical stator, a circular rotor which iseccentrically positioned in the stator and is providedwith twoor more outwardly spring-pressed vanes for sliding engagement with the surrounding cylindrical wall of the stator,

an arcuate seat in said wall of the same radius of curvature as the rotor, in-which'seatthe rotor turnsmneans for supplying'oil to the crescentshaped pumping chamber present between the stator and, rotor, an inlet port in the pumping chamber at the low pressure side oi'the seat,

circumferentiallyextending grooves in the opposed side walls of the pumping chamber at the high pressure side of the seat, which grooves extend back away from the seat along the path of approach of the vanes, inwardly extending grooves in the opposed side walls of the pumping chamber with their outer ends in communication with the'ends of the circumierentially extending grooves which are nearer the seat, a cross groove in the cylindrical peripheral wall of the stator at the edge of the high pressure side or the seat in communication at lts'ends with the connecting endsor the circumferentially extending grooves and inwardly extending grooves, and an outlet port in communication with one or the 11. In a rotary oil sealed vacuum pump for producing extremely high vacuums, a casing containing roughing and finishing stages arranged alongside each other, said casing being characterized by a center plate between the stages and end plates at the far sides of the stages, a drive shaitiournaled in aligning bearing apertures in the center plate and endplates, rotors on the shaft in both stages forming with the surrounding stage and returning itto the same, an outlet.

port from the finishing stage opening directly through one of the double walls of the center, 'plate into the center chamber, an inlet port for the roughing stage opening directly into the roughing stage from the center chamber through the other double wall of the center plate, and separate means isolated from direct communication with the inlet port of the finishing stage 7 for conducting oil from the center chamber back to the finishing stage.

12. A vacuum pump of the construction described in claim 11. in which the casing is provided at one side with an opening in communication with the chamber in the center plate, and in which'a cover plate is detachably secured to the casing over said-opening in fluid-tight'assm- JOHN DUBRovm' elation with the same. 

